28 lines
986 B
Markdown
28 lines
986 B
Markdown
Evaluate Expressions Only
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========================
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{{#include ../links.md}}
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Sometimes a use case does not require a full-blown scripting _language_, but only needs to evaluate _expressions_.
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In these cases, use the `Engine::compile_expression` and `Engine::eval_expression` methods or their `_with_scope` variants.
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```rust
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let result = engine.eval_expression::<i64>("2 + (10 + 10) * 2")?;
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```
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When evaluating _expressions_, no full-blown statement (e.g. `if`, `while`, `for`, `fn`) - not even variable assignment -
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is supported and will be considered parse errors when encountered.
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[Closures] and [anonymous functions] are also not supported because in the background they compile to functions.
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```rust
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// The following are all syntax errors because the script is not an expression.
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engine.eval_expression::<()>("x = 42")?;
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let ast = engine.compile_expression("let x = 42")?;
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let result = engine.eval_expression_with_scope::<i64>(&mut scope, "if x { 42 } else { 123 }")?;
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```
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